Polycarbonate has been a commercially available thermoplastic for many years. It is known for its high impact strength and clarity. As with all commercially useful materials there are continual efforts to improve its properties. Quite often small technical improvements in physical or chemical properties have large ramifications in the marketplace.
One area of particular commercial importance is improvement of the stability of polymers. Example of such stability are: thermal stability, rheological stability, color stability, oxidative stability, ozonation stability, light stability, ultraviolet light stability, gamma radiation stability, and hydrolytic stability. In each case specific chemical agents have been identified that improve one of these specific types of commercially important stability parameters. This can result in a large number of similar products that differ only in their relative stability to various different conditions. The process of developing compositions that only meet single requirements excludes the applications that have multiple stability requirements. As is taught for example by Fukawa, et al. in U.S. Pat. No. 5,225,526 "there have not yet been obtained any stabilized compositions which are free from all of the noted problems: heat resistance, hot water resistance and coloration in recycle molding". Thus, Fukawa et al. recognize that the systematic approach to improved stability across more than a single parameter or requirement is recognized as a serious deficiency in the prior art.
The problem of polymer degradation is typically managed by the addition of various stabilizers and additives to the polymer. Since the art is not systematic and predictive, these solutions are varied and many and do not provide a consistent basis for prediction of effects as the polymer to be stabilized is varied or as chemical changes are made to the stabilizer compounds used. The art thus contains conflicting statements and teachings.